Fix a bug in Mtftp6 retransmission mechanism of the ACK.

Signed-off-by: Ari Zigler <ariz@mellanox.com>
Reviewed-by: Ouyang Qian <qian.ouyang@intel.com> 
Reviewed-by: Fu Siyuan <siyuan.fu@intel.com>


git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@14450 6f19259b-4bc3-4df7-8a09-765794883524

NetworkPkg/Mtftp6Dxe/Mtftp6Rrq.c

@@ -59,6 +59,7 @@ Mtftp6RrqSendAck (
   // Reset current retry count of the instance.
   //
   Instance->CurRetry = 0;
+  Instance->LastPacket = Packet;
 
   return Mtftp6TransmitPacket (Instance, Packet);
 }